Flurry is installed by SmartPhone developers to monitor the usage of their applications. So successful has it been that they are installed on 85% of all smartphones and track over 15 Billion user sessions per month across iOS, Android, BlackBerry, Windows Phone and J2ME.

For this report, Flurry used data from over 45,000 companies and 85,000 applications.

I recommend you read the report but if you would like a couple of take-aways I liked,

Reviewing the chart, we note that the UK leads in [6 month app] retention with 38%, followed by France at 37%, Germany at 34% and then Spain and Italy at 32% and 31.5%, respectively. Generally, we see a correlation between the maturity of a given market and app retention. We observe that consumers typically try several apps before they settle into using a group of favorites, which they then use several times per week, even per day. In less developed countries, we often see much more app experimentation. The five countries we review for this report are clearly all highly developed economies.

and

To underscore just how aggressively this channel is growing, if we assumed the growth of smartphone adoption continued at their current rates, [UK, France, Germany, Italy, Spain] would have full smartphone penetration in just over two years.